kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 63 insertions, 0 deletions

diff --git a/net/tls/tls_proc.c b/net/tls/tls_proc.c
new file mode 100644
index 000000000..4012c4372
--- /dev/null
+++ b/net/tls/tls_proc.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/* Copyright (C) 2019 Netronome Systems, Inc. */
+
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <net/snmp.h>
+#include <net/tls.h>
+
+#include "tls.h"
+
+#ifdef CONFIG_PROC_FS
+static const struct snmp_mib tls_mib_list[] = {
+	SNMP_MIB_ITEM("TlsCurrTxSw", LINUX_MIB_TLSCURRTXSW),
+	SNMP_MIB_ITEM("TlsCurrRxSw", LINUX_MIB_TLSCURRRXSW),
+	SNMP_MIB_ITEM("TlsCurrTxDevice", LINUX_MIB_TLSCURRTXDEVICE),
+	SNMP_MIB_ITEM("TlsCurrRxDevice", LINUX_MIB_TLSCURRRXDEVICE),
+	SNMP_MIB_ITEM("TlsTxSw", LINUX_MIB_TLSTXSW),
+	SNMP_MIB_ITEM("TlsRxSw", LINUX_MIB_TLSRXSW),
+	SNMP_MIB_ITEM("TlsTxDevice", LINUX_MIB_TLSTXDEVICE),
+	SNMP_MIB_ITEM("TlsRxDevice", LINUX_MIB_TLSRXDEVICE),
+	SNMP_MIB_ITEM("TlsDecryptError", LINUX_MIB_TLSDECRYPTERROR),
+	SNMP_MIB_ITEM("TlsRxDeviceResync", LINUX_MIB_TLSRXDEVICERESYNC),
+	SNMP_MIB_ITEM("TlsDecryptRetry", LINUX_MIB_TLSDECRYPTRETRY),
+	SNMP_MIB_ITEM("TlsRxNoPadViolation", LINUX_MIB_TLSRXNOPADVIOL),
+	SNMP_MIB_ITEM("TlsRxRekeyOk", LINUX_MIB_TLSRXREKEYOK),
+	SNMP_MIB_ITEM("TlsRxRekeyError", LINUX_MIB_TLSRXREKEYERROR),
+	SNMP_MIB_ITEM("TlsTxRekeyOk", LINUX_MIB_TLSTXREKEYOK),
+	SNMP_MIB_ITEM("TlsTxRekeyError", LINUX_MIB_TLSTXREKEYERROR),
+	SNMP_MIB_ITEM("TlsRxRekeyReceived", LINUX_MIB_TLSRXREKEYRECEIVED),
+};
+
+static int tls_statistics_seq_show(struct seq_file *seq, void *v)
+{
+	unsigned long buf[ARRAY_SIZE(tls_mib_list)];
+	const int cnt = ARRAY_SIZE(tls_mib_list);
+	struct net *net = seq->private;
+	int i;
+
+	memset(buf, 0, sizeof(buf));
+	snmp_get_cpu_field_batch_cnt(buf, tls_mib_list, cnt,
+				     net->mib.tls_statistics);
+	for (i = 0; i < cnt; i++)
+		seq_printf(seq, "%-32s\t%lu\n", tls_mib_list[i].name, buf[i]);
+
+	return 0;
+}
+#endif
+
+int __net_init tls_proc_init(struct net *net)
+{
+#ifdef CONFIG_PROC_FS
+	if (!proc_create_net_single("tls_stat", 0444, net->proc_net,
+				    tls_statistics_seq_show, NULL))
+		return -ENOMEM;
+#endif /* CONFIG_PROC_FS */
+
+	return 0;
+}
+
+void __net_exit tls_proc_fini(struct net *net)
+{
+	remove_proc_entry("tls_stat", net->proc_net);
+}